1. Field of the Invention
The present invention relates to an internal combustion engine having a combustion heater.
2. Description of the Prior Art
For example, Japanese Patent Application Laid-Open Publication No. 62-75069 discloses an art, in which an intake system of an internal combustion engine is provided with a combustion heater separately from an internal combustion engine body, raising a temperature of engine cooling water contained in a water jacket of the internal combustion engine by utilizing the combustion heat of the combustion heater, and thereby to attain the speeding up of warming the engine and enhancing a starting performance.
According to this art disclosed in the above Publication, the pipe is inserted into the water jacket of the internal combustion engine, and the combustion gas emitted from the combustion heater is allowed to flow into this pipe before starting up the engine. Then, the heat held by the combustion gas is thereby transmitted to the engine cooling water, and hence the temperature of the engine cooling water can be increased up to a desired temperature prescribed for each internal combustion engine by regulating a thermal quantity given to the engine cooling water.
"The desired temperature of the engine cooling water" implies a temperature enough to speed up the warm-up of the internal combustion engine and to enhance the starting characteristic thereof when the engine cooling water is warmed by the combustion heater and reaches this temperature.
It can be considered to enhance performances of a temperature raising mechanism for raising temperatures of the car room heater and of the internal combustion engine itself, and an intake air heating device and other temperature raising devices by raising a temperature of heat transmission fluid which is represented by the engine cooling water which has its temperature increased by the combustion heater as disclosed in the above Publication. In this case, in order to increase a heat exchange rate of the combustion heater to the heat transmission fluid, it may be sufficient to make a heat exchanging member of the combustion heater thin and elongate. In this instance, however, there might arise a problem that a water-flow resistance augments so that a flow rate to the temperature raising device is reduced or causes an increase of a drive loss of a pump for circulating the heat transmission fluid. Therefore, there must be naturally a limit for increasing the heat exchange rate. In such a case, since a sufficient heat exchange is not made, the temperature of the combustion gas of the combustion heater, which is introduced into the intake system of the internal combustion engine, inevitably becomes comparatively high. Hence, there might be caused thermal damages to the structures of the intake system.
Further, as demanded with times, decrease of a compression ratio of the internal combustion engine, namely, a low compression ratio, is required. However, this involves a problem that the starting characteristic of the internal combustion engine at a low temperature tends to decline.
Moreover, if trying to decrease the compression ratio of the internal combustion engine, the warm-up of the oil is delayed at the time of warming up the internal combustion engine because of a small exothermic quantity of the engine, resulting in such a problem that an engine friction becomes large and a fuel efficiency declines.